A newly discovered planet with 7 times the mass of Earth orbits in the habitable or “Goldilocks” zone around a 7th magnitude star HD 40307 in the southern constellation Pictor the Easel. Habitable doesn’t necessarily imply life could take spring forth on this weightier version of Earth, but it does mean the planet orbits at just the right distance for liquid water to be stable on its surface. Goldilocks refers to conditions being neither too hot nor too cold but “just right”.
HD 40307 is an orange-colored star a little smaller, less massive and cooler than the sun located 42 light years from Earth. Unremarkable perhaps except for one little detail: this sun is orbited by six planets. Five of them are close in and hotter than Hades, but the sixth orbits at about the same distance Earth does from the sun. While you’d weigh considerably more there due its greater mass, floating in an ocean to relieve the inevitable back pain is theoretically possible.
Video with further description of the HD 40307 solar system
HD 40307 is one of three new super-Earths (rocky extrasolar planets at least several times more massive than Earth) discovered around the star but the only potentially hospitable one. An international team, including Carnegie Institution for Science co-author Paul Butler, was led by Mikko Tuomi of the University of Hertfordshire and Guillem Anglada-Escudé of the University of Göttingen. The researchers re-analyzed the spectra or fingerprints of the star’s light made with the European Southern Observatory’s HARPS spectrograph using new software. Hidden in the data were signatures of the three additional planets.
HD 40307g belongs to a small but growing list of Earth-like planets orbiting a comfortable distance from their host stars. Most of the confirmed 849 extrasolar planets currently known are nicknamed “hot Jupiters” for good reason. They’re massive and orbit close to their suns, exerting measurable gravitational wobbles in their host stars that our equipment can detect. Smaller worlds orbiting at more habitable distances tug but a little and are much more difficult to identify.
In 1988 Canadian astronomers Bruce Campbell, G. A. H. Walker, and Stephenson Yang reported gravitational wobbles of the star Gamma in the constellation Cepheus and cautiously attributed it to a planet. Their observations weren’t confirmed until 2003, making Gamma Cephei Ab the first extrasolar planet discovered. The first definitive discovery of a pair of planets found orbiting a dense, rapidly-spinning star called a pulsar on April 21, 1992.
We’ve come far quickly. I suspect we’ll find a planet with signatures of life’s best indicators – water, methane and oxygen – in our lifetimes. Will it be HD 40307g?